FRA's preliminary investigation determined the derailment was caused by broken lag bolts leading to a wide track gauge. Investigators found multiple lag bolts in the track section were broken and sheared, leading to tie plates loosening from ties and allowing the rails to be pushed outwards as trains moved across them.

Jun 27, 2016

The Federal Railroad Administration posted its preliminary findings on the cause of a June 3 derailment near Mosier, Ore., of a Union Pacific train that was carrying Bakken crude oil for U.S. Oil & Refining Company. The incident at 12:15 p.m. PDT caused 16 tank cars to derail at a point when the train was moving at about 25 mph. The speed restriction for that track section is 30 mph because of the curvature of the track, FRA reported. About 42,000 gallons of crude oil spilled as a result.

The train originated in New Town, N.D., and was destined for Tacoma, Wash. The train consisted of two head-end locomotives, one distributed power locomotive at the rear, two buffer cars, and 94 tank cars loaded with Bakken crude. FRA's report said Dakota Plains loaded the tank cars for U.S. Oil in New Town and the crude oil had a vapor pressure of 9.2 psi measured at the loading facility. The tank cars "were general purpose specification DOT-111 tanks cars, modified to the Association of American Railroads (AAR) CPC-1232 standard. The cars were equipped with full-height head shields and metal jackets with insulation. The cars did not have thermal protection," it said, adding that these tank cars are commonly referred to as "jacketed 1232s."

"During the derailment, a coupler struck one tank car, mechanically puncturing it. This puncture allowed crude oil to come into contact with an ignition source, leading to a fire that burned for approximately 14 hours. Four cars were eventually involved in the fire," the reported said. "The four tank cars involved in the fire were the punctured car, and three additional tank cars – two that had their bottom outlet valves sheared off in the derailment, and one car with the gasket melted out from under the manway cover."

FRA's preliminary investigation determined the derailment was caused by broken lag bolts leading to a wide track gauge. Investigators found multiple lag bolts in the track section were broken and sheared, leading to tie plates loosening from ties and allowing the rails to be pushed outwards as trains moved across them.

The tank cars involved in the derailment performed as expected in the incident based on tank car performance metrics, according to the agency, which reported that its Office of Research and Development conducted simulations of a derailment similar to this one and found that applying the brakes uniformly and instantaneously would have provided additional train control, potentially shortening the stopping distance and leading to a less severe derailment.

"Unless or until additional details come to light, FRA has made the preliminary determination that Union Pacific's failure to maintain its track and track equipment resulted in the derailment. Broken and sheared lag bolts, while difficult to detect by high-rail, are more detectable by walking inspection combined with indications of movement in the rail or track structure and/or uneven rail wear, and are critically important to resolve quickly," the agency stated. It is evaluating potential enforcement actions, including violations, and other actions to ensure Union Pacific's compliance with applicable safety regulations.